Sitting on the train reading comedian Mark Thomas's book, Extreme Rambling: Walking Israel's Barrier, I'm approached by a young woman who wants to know where to get it. "I'm a fan," she says, "and so is my brother, who lives in Israel. I think it will be interesting, not that there'll be any surprises. He is so pro-Palestinian."

Mark Thomas laughs when I tell him about the exchange: "I'm not pro-Palestinian; I'm just pro-justice." And, he says, he has long been interested in the questions and contradictions besetting the conflict: "When will a people be free and what must a country do to protect itself from suicide bombers?

"I have sympathy with the Palestinian cause but despised the methods of the Second Intifada and for a while switched off about the whole issue. But the war on Gaza in 2008 changed all that."

And so, armed with plasters, white spirit to keep his feet hard, and Kendal Mint Cake, he set off, aware that, unlike his past campaigns (eg stopping a hydro-electric dam being built in Turkey), this one would be unlikely to produce tangible results.

Predictably, Thomas's encounters with Israelis on his 51-day trip were not always comfortable and, along with being tear-gassed and held in custody, he details his discomfort around settlers "on the Israeli side of the fence where the grass is literally greener… you'd be hard-pressed not to notice the sprinklers on Israeli farms while on the Palestinian side there's thin irrigation tubing between the plastic greenhouses."

Though Thomas's book - and the stage show based on it - is undeniably weighted towards the plight of the Palestinians, it is not a total whitewash. Israeli views and - often moving - stories are included. "I open the book with an Israeli," he says. This is Dror, a shopkeeper in Sdei Trumot, a village north of the West Bank. "Between the shop porch and the highway is a flower bed where a white memorial stone marks the spot where his father was killed by a suicide bomber seven years ago. He was a farmer who ate, drank and worked with Palestinians, but good relations are over now. What interested me most was Dror's take on the Fence: 'If they want to come to make an explosion, they come; the Fence will make it harder but they will find a way.'"

Thomas does strike one note of regret: "A group of Palestinian kids were throwing pebbles at us and calling me, Yahod (Jew) and I told our interpreter to tell them I wasn't Jewish for which I am most ashamed. I'm not Jewish but know something about Jewish culture and have a mate who advises me on Yiddish. But, at that moment, fear took over. When something is frightening, things unravel very quickly."

So did the ramble provide answers to his questions? "I remember meeting this lovely translator for the border patrol and she asked me if I was trying to find a solution. I laughed and told her. 'That's your job. I can't tell you what to do. You have to work it out.' Frankly, I've never been to a place before where so many people answer questions with questions."